1. Field of the Invention
The present invention relates to a method and arrangement for hydraulic conveying of solids in general, and more particularly to a hydraulic conveying device for solids of different specific weights, such as coal and rock, and to a hydraulic conveying method.
2. The Prior Art
Various hydraulic conveying arrangements of the type here under consideration are already known. Generally speaking these employ chambers into which a slurry is introduced at substantially atmospheric pressure, to be discharged therefrom at an elevated pressure by a pressurized hydraulic fluid, such as readily available water.
Such arrangements are used, for instance, for conveying an aqueous slurry of coal particles from an underground excavation to the surface. An important advantage of such an arrangement is that the slurry is fed into the respective chamber at substantially atmospheric pressure so that the coal particles accumulate in the chamber; this means that conventional slurry pumps which are incapable of generating any substantial pressure or velocity head can nevertheless be used for feeding the slurry into the chamber. On the other hand, once the chamber is filled with the slurry, and particularly with the coal particles, high-pressure hydraulic fluid, such as water, is admitted into the chamber, entrains the coal particles and discharges them in form of a slurry into a discharge conduit. Inasmuch as the pressurized water or similar fluid does not contain any solid particles to speak of, high-output pumps, such as centrifugal pumps, which are sensitive to solid impurities contained in the fluid being pumped, can be used for supplying the pressurized water to the chamber from which the coal particles are to be discharged. Since such high-output pumps generate substantial velocity, and particularly pressure head, the slurry discharged from the chamber into the discharge conduit has sufficient energy to overcome substantial elevational differences and/or to be conveyed over substantial distances. Such an arrangement includes a plurality of valves which are selectively operated to establish communication of the chamber with either the source of slurry, or the source of the pressurized fluid on the one hand, and with the discharge conduit on the other hand.
It will be appreciated that when only one such chamber is utilized, the operation of the arrangement can only be intermittent. This means that, when the chamber is being filled, no flow exists in the discharge conduit which, of course, is very disadvantageous, particularly since the particles entrained in the water will settle and thus possibly clog the discharge conduit.
Therefore, it has already been proposed to use at least two chambers which are alternatingly filled and discharged, whereby continuous flow is obtained in the discharge conduit. The chambers may be filled and discharged concurrently, that is, both the slurry and the pressurized hydraulic fluid may be admitted into each chamber at the same end thereof, and the slurry may be discharged from the respective chamber at the other end thereof. However, experience has shown that it is more advantageous to operate the chambers in countercurrent, that is, to admit and discharge the slurry at one end of the respective chamber, and admit the pressurized hydraulic fluid at the other end of each respective chamber.
However, when such an arrangement is to be used for conveying material from an underground excavation to the surface, it has been found that some difficulties arise in connection with the operation of the arrangement, particularly due to the fact that the material to be conveyed to the surface includes not only coal particles, but also rock particles from the strata surrounding the seam of coal. The material to be conveyed comprises, in addition to particles of different specific weights, also particles of different sizes and thus of different weights. When the particulate material is conveyed through the discharge conduit to the surface, by being entrained with the pressurized hydraulic fluid, the result of the different specific weights, sizes, and weights of the particles is that some of the particles will move through the discharge conduit at a slower speed than other particles. Thus, experience with this conventional type of arrangement has shown that under certain conditions the differences in speeds of the particles may result in accumulation of the particles in some regions of the discharge conduit, whereby the conduit may become clogged. Because of this danger the conventional arrangements for conveying solids of this type have not yet found widespread acceptance in the mining industry.
The efficiency of a hydraulic conveying system increases with the increasing length of the chambers, particularly since the quantity of pressurized hydraulic fluid which is needed to discharge the contents of the chamber into the discharge conduit remains, for all intents and purposes, virtually the same for all lengths of the chambers. This, of course, means that the concentration of the slurry increases with the increasing length of the respective chamber. Also, the filling time for a longer chamber is longer than for a shorter chamber so that the admitting and discharging valve need not be switched as often with a longer chamber as with a shorter chamber, which means that the valves need not be replaced or repaired as often. This improves the efficiency of such hydraulic limitations to the increase in length of the chamber, resulting, mainly from the limited capacity of the slurry pump. The elevation head of the slurry pump determines the permissible length of the chambers, due to the fact that the filling speed of the chambers must be held constant. Inasmuch as the filling speed of the chamber depends on the concentration of the slurry, the fact that the slurry may include particles of different specific weights, sizes and weights will have a profound influence upon the filling speed of the chamber and thus on the efficiency of the conveying arrangement.